{-|
Functions for ensuring transactions and journals are balanced.
-}

{-# LANGUAGE LambdaCase          #-}
{-# LANGUAGE NamedFieldPuns      #-}
{-# LANGUAGE OverloadedStrings   #-}
{-# LANGUAGE PackageImports      #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TemplateHaskell     #-}

module Hledger.Data.Balancing
( -- * BalancingOpts
  BalancingOpts(..)
, HasBalancingOpts(..)
, defbalancingopts
  -- * transaction balancing
, isTransactionBalanced
, balanceTransaction
, balanceTransactionHelper
, annotateErrorWithTransaction
  -- * journal balancing
, journalBalanceTransactions
, journalCheckBalanceAssertions
  -- * tests
, tests_Balancing
)
where

import Control.Monad.Except (ExceptT(..), runExceptT, throwError)
import "extra" Control.Monad.Extra (whenM)
import Control.Monad.Reader as R
import Control.Monad.ST (ST, runST)
import Data.Array.ST (STArray, getElems, newListArray, writeArray)
import Data.Foldable (asum)
import Data.Function ((&))
import qualified Data.HashTable.Class as H (toList)
import qualified Data.HashTable.ST.Cuckoo as H
import Data.List (intercalate, partition, sortOn)
import Data.List.Extra (nubSort)
import Data.Maybe (fromJust, fromMaybe, isJust, isNothing, mapMaybe)
import qualified Data.Set as S
import qualified Data.Text as T
import Data.Time.Calendar (fromGregorian)
import qualified Data.Map as M
import Safe (headDef)
import Text.Printf (printf)

import Hledger.Utils
import Hledger.Data.Types
import Hledger.Data.AccountName (isAccountNamePrefixOf)
import Hledger.Data.Amount
import Hledger.Data.Dates (showDate)
import Hledger.Data.Journal
import Hledger.Data.Posting
import Hledger.Data.Transaction


data BalancingOpts = BalancingOpts
  { ignore_assertions_        :: Bool  -- ^ Ignore balance assertions
  , infer_transaction_prices_ :: Bool  -- ^ Infer prices in unbalanced multicommodity amounts
  , commodity_styles_         :: Maybe (M.Map CommoditySymbol AmountStyle)  -- ^ commodity display styles
  } deriving (Show)

defbalancingopts :: BalancingOpts
defbalancingopts = BalancingOpts
  { ignore_assertions_        = False
  , infer_transaction_prices_ = True
  , commodity_styles_         = Nothing
  }

-- | Check that this transaction would appear balanced to a human when displayed.
-- On success, returns the empty list, otherwise one or more error messages.
--
-- In more detail:
-- For the real postings, and separately for the balanced virtual postings:
--
-- 1. Convert amounts to cost where possible
--
-- 2. When there are two or more non-zero amounts
--    (appearing non-zero when displayed, using the given display styles if provided),
--    are they a mix of positives and negatives ?
--    This is checked separately to give a clearer error message.
--    (Best effort; could be confused by postings with multicommodity amounts.)
--
-- 3. Does the amounts' sum appear non-zero when displayed ?
--    (using the given display styles if provided)
--
transactionCheckBalanced :: BalancingOpts -> Transaction -> [String]
transactionCheckBalanced BalancingOpts{commodity_styles_} t = errs
  where
    (rps, bvps) = foldr partitionPosting ([], []) $ tpostings t
      where
        partitionPosting p ~(l, r) = case ptype p of
            RegularPosting         -> (p:l, r)
            BalancedVirtualPosting -> (l, p:r)
            VirtualPosting         -> (l, r)

    -- check for mixed signs, detecting nonzeros at display precision
    canonicalise = maybe id canonicaliseMixedAmount commodity_styles_
    signsOk ps =
      case filter (not.mixedAmountLooksZero) $ map (canonicalise.mixedAmountCost.pamount) ps of
        nonzeros | length nonzeros >= 2
                   -> length (nubSort $ mapMaybe isNegativeMixedAmount nonzeros) > 1
        _          -> True
    (rsignsok, bvsignsok)       = (signsOk rps, signsOk bvps)

    -- check for zero sum, at display precision
    (rsum, bvsum)               = (sumPostings rps, sumPostings bvps)
    (rsumcost, bvsumcost)       = (mixedAmountCost rsum, mixedAmountCost bvsum)
    (rsumdisplay, bvsumdisplay) = (canonicalise rsumcost, canonicalise bvsumcost)
    (rsumok, bvsumok)           = (mixedAmountLooksZero rsumdisplay, mixedAmountLooksZero bvsumdisplay)

    -- generate error messages, showing amounts with their original precision
    errs = filter (not.null) [rmsg, bvmsg]
      where
        rmsg
          | rsumok        = ""
          | not rsignsok  = "real postings all have the same sign"
          | otherwise     = "real postings' sum should be 0 but is: " ++ showMixedAmount rsumcost
        bvmsg
          | bvsumok       = ""
          | not bvsignsok = "balanced virtual postings all have the same sign"
          | otherwise     = "balanced virtual postings' sum should be 0 but is: " ++ showMixedAmount bvsumcost

-- | Legacy form of transactionCheckBalanced.
isTransactionBalanced :: BalancingOpts -> Transaction -> Bool
isTransactionBalanced bopts = null . transactionCheckBalanced bopts

-- | Balance this transaction, ensuring that its postings
-- (and its balanced virtual postings) sum to 0,
-- by inferring a missing amount or conversion price(s) if needed.
-- Or if balancing is not possible, because the amounts don't sum to 0 or
-- because there's more than one missing amount, return an error message.
--
-- Transactions with balance assignments can have more than one
-- missing amount; to balance those you should use the more powerful
-- journalBalanceTransactions.
--
-- The "sum to 0" test is done using commodity display precisions,
-- if provided, so that the result agrees with the numbers users can see.
--
balanceTransaction ::
     BalancingOpts
  -> Transaction
  -> Either String Transaction
balanceTransaction bopts = fmap fst . balanceTransactionHelper bopts

-- | Helper used by balanceTransaction and balanceTransactionWithBalanceAssignmentAndCheckAssertionsB;
-- use one of those instead. It also returns a list of accounts
-- and amounts that were inferred.
balanceTransactionHelper ::
     BalancingOpts
  -> Transaction
  -> Either String (Transaction, [(AccountName, MixedAmount)])
balanceTransactionHelper bopts t = do
  (t', inferredamtsandaccts) <- inferBalancingAmount (fromMaybe M.empty $ commodity_styles_ bopts) $
    if infer_transaction_prices_ bopts then inferBalancingPrices t else t
  case transactionCheckBalanced bopts t' of
    []   -> Right (txnTieKnot t', inferredamtsandaccts)
    errs -> Left $ transactionBalanceError t' errs

-- | Generate a transaction balancing error message, given the transaction
-- and one or more suberror messages.
transactionBalanceError :: Transaction -> [String] -> String
transactionBalanceError t errs =
  annotateErrorWithTransaction t $
  intercalate "\n" $ "could not balance this transaction:" : errs

annotateErrorWithTransaction :: Transaction -> String -> String
annotateErrorWithTransaction t s =
  unlines [ showGenericSourcePos $ tsourcepos t, s
          , T.unpack . T.stripEnd $ showTransaction t
          ]

-- | Infer up to one missing amount for this transactions's real postings, and
-- likewise for its balanced virtual postings, if needed; or return an error
-- message if we can't. Returns the updated transaction and any inferred posting amounts,
-- with the corresponding accounts, in order).
--
-- We can infer a missing amount when there are multiple postings and exactly
-- one of them is amountless. If the amounts had price(s) the inferred amount
-- have the same price(s), and will be converted to the price commodity.
inferBalancingAmount ::
     M.Map CommoditySymbol AmountStyle -- ^ commodity display styles
  -> Transaction
  -> Either String (Transaction, [(AccountName, MixedAmount)])
inferBalancingAmount styles t@Transaction{tpostings=ps}
  | length amountlessrealps > 1
      = Left $ transactionBalanceError t
        ["can't have more than one real posting with no amount"
        ,"(remember to put two or more spaces between account and amount)"]
  | length amountlessbvps > 1
      = Left $ transactionBalanceError t
        ["can't have more than one balanced virtual posting with no amount"
        ,"(remember to put two or more spaces between account and amount)"]
  | otherwise
      = let psandinferredamts = map inferamount ps
            inferredacctsandamts = [(paccount p, amt) | (p, Just amt) <- psandinferredamts]
        in Right (t{tpostings=map fst psandinferredamts}, inferredacctsandamts)
  where
    (amountfulrealps, amountlessrealps) = partition hasAmount (realPostings t)
    realsum = sumPostings amountfulrealps
    (amountfulbvps, amountlessbvps) = partition hasAmount (balancedVirtualPostings t)
    bvsum = sumPostings amountfulbvps

    inferamount :: Posting -> (Posting, Maybe MixedAmount)
    inferamount p =
      let
        minferredamt = case ptype p of
          RegularPosting         | not (hasAmount p) -> Just realsum
          BalancedVirtualPosting | not (hasAmount p) -> Just bvsum
          _                                          -> Nothing
      in
        case minferredamt of
          Nothing -> (p, Nothing)
          Just a  -> (p{pamount=a', poriginal=Just $ originalPosting p}, Just a')
            where
              -- Inferred amounts are converted to cost.
              -- Also ensure the new amount has the standard style for its commodity
              -- (since the main amount styling pass happened before this balancing pass);
              a' = styleMixedAmount styles . mixedAmountCost $ maNegate a

-- | Infer prices for this transaction's posting amounts, if needed to make
-- the postings balance, and if possible. This is done once for the real
-- postings and again (separately) for the balanced virtual postings. When
-- it's not possible, the transaction is left unchanged.
--
-- The simplest example is a transaction with two postings, each in a
-- different commodity, with no prices specified. In this case we'll add a
-- price to the first posting such that it can be converted to the commodity
-- of the second posting (with -B), and such that the postings balance.
--
-- In general, we can infer a conversion price when the sum of posting amounts
-- contains exactly two different commodities and no explicit prices.  Also
-- all postings are expected to contain an explicit amount (no missing
-- amounts) in a single commodity. Otherwise no price inferring is attempted.
--
-- The transaction itself could contain more than two commodities, and/or
-- prices, if they cancel out; what matters is that the sum of posting amounts
-- contains exactly two commodities and zero prices.
--
-- There can also be more than two postings in either of the commodities.
--
-- We want to avoid excessive display of digits when the calculated price is
-- an irrational number, while hopefully also ensuring the displayed numbers
-- make sense if the user does a manual calculation. This is (mostly) achieved
-- in two ways:
--
-- - when there is only one posting in the "from" commodity, a total price
--   (@@) is used, and all available decimal digits are shown
--
-- - otherwise, a suitable averaged unit price (@) is applied to the relevant
--   postings, with display precision equal to the summed display precisions
--   of the two commodities being converted between, or 2, whichever is larger.
--
-- (We don't always calculate a good-looking display precision for unit prices
-- when the commodity display precisions are low, eg when a journal doesn't
-- use any decimal places. The minimum of 2 helps make the prices shown by the
-- print command a bit less surprising in this case. Could do better.)
--
inferBalancingPrices :: Transaction -> Transaction
inferBalancingPrices t@Transaction{tpostings=ps} = t{tpostings=ps'}
  where
    ps' = map (priceInferrerFor t BalancedVirtualPosting . priceInferrerFor t RegularPosting) ps

-- | Generate a posting update function which assigns a suitable balancing
-- price to the posting, if and as appropriate for the given transaction and
-- posting type (real or balanced virtual). If we cannot or should not infer
-- prices, just act as the identity on postings.
priceInferrerFor :: Transaction -> PostingType -> (Posting -> Posting)
priceInferrerFor t pt = maybe id inferprice inferFromAndTo
  where
    postings     = filter ((==pt).ptype) $ tpostings t
    pcommodities = map acommodity $ concatMap (amounts . pamount) postings
    sumamounts   = amounts $ sumPostings postings  -- amounts normalises to one amount per commodity & price

    -- We can infer prices if there are no prices given, exactly two commodities in the normalised
    -- sum of postings in this transaction, and these two have opposite signs. The amount we are
    -- converting from is the first commodity to appear in the ordered list of postings, and the
    -- commodity we are converting to is the other. If we cannot infer prices, return Nothing.
    inferFromAndTo = case sumamounts of
      [a,b] | noprices, oppositesigns -> asum $ map orderIfMatches pcommodities
        where
          noprices      = all (isNothing . aprice) sumamounts
          oppositesigns = signum (aquantity a) /= signum (aquantity b)
          orderIfMatches x | x == acommodity a = Just (a,b)
                           | x == acommodity b = Just (b,a)
                           | otherwise         = Nothing
      _ -> Nothing

    -- For each posting, if the posting type matches, there is only a single amount in the posting,
    -- and the commodity of the amount matches the amount we're converting from,
    -- then set its price based on the ratio between fromamount and toamount.
    inferprice (fromamount, toamount) posting
        | [a] <- amounts (pamount posting), ptype posting == pt, acommodity a == acommodity fromamount
            = posting{ pamount   = mixedAmount a{aprice=Just conversionprice}
                     , poriginal = Just $ originalPosting posting }
        | otherwise = posting
      where
        -- If only one Amount in the posting list matches fromamount we can use TotalPrice.
        -- Otherwise divide the conversion equally among the Amounts by using a unit price.
        conversionprice = case filter (== acommodity fromamount) pcommodities of
            [_] -> TotalPrice $ negate toamount
            _   -> UnitPrice  $ negate unitprice `withPrecision` unitprecision

        unitprice     = aquantity fromamount `divideAmount` toamount
        unitprecision = case (asprecision $ astyle fromamount, asprecision $ astyle toamount) of
            (Precision a, Precision b) -> Precision . max 2 $ saturatedAdd a b
            _                          -> NaturalPrecision
        saturatedAdd a b = if maxBound - a < b then maxBound else a + b


-- | Check any balance assertions in the journal and return an error message
-- if any of them fail (or if the transaction balancing they require fails).
journalCheckBalanceAssertions :: Journal -> Maybe String
journalCheckBalanceAssertions = either Just (const Nothing) . journalBalanceTransactions defbalancingopts

-- "Transaction balancing", including: inferring missing amounts,
-- applying balance assignments, checking transaction balancedness,
-- checking balance assertions, respecting posting dates. These things
-- are all interdependent.
-- WARN tricky algorithm and code ahead. 
--
-- Code overview as of 20190219, this could/should be simplified/documented more:
--  parseAndFinaliseJournal['] (Cli/Utils.hs), journalAddForecast (Common.hs), journalAddBudgetGoalTransactions (BudgetReport.hs), tests (BalanceReport.hs)
--   journalBalanceTransactions
--    runST
--     runExceptT
--      balanceTransaction (Transaction.hs)
--       balanceTransactionHelper
--      runReaderT
--       balanceTransactionAndCheckAssertionsB
--        addAmountAndCheckAssertionB
--        addOrAssignAmountAndCheckAssertionB
--        balanceTransactionHelper (Transaction.hs)
--  uiCheckBalanceAssertions d ui@UIState{aopts=UIOpts{cliopts_=copts}, ajournal=j} (ErrorScreen.hs)
--   journalCheckBalanceAssertions
--    journalBalanceTransactions
--  transactionWizard, postingsBalanced (Add.hs), tests (Transaction.hs)
--   balanceTransaction (Transaction.hs)  XXX hledger add won't allow balance assignments + missing amount ?

-- | Monad used for statefully balancing/amount-inferring/assertion-checking
-- a sequence of transactions.
-- Perhaps can be simplified, or would a different ordering of layers make sense ?
-- If you see a way, let us know.
type Balancing s = ReaderT (BalancingState s) (ExceptT String (ST s))

-- | The state used while balancing a sequence of transactions.
data BalancingState s = BalancingState {
   -- read only
   bsStyles       :: Maybe (M.Map CommoditySymbol AmountStyle)  -- ^ commodity display styles
  ,bsUnassignable :: S.Set AccountName                          -- ^ accounts in which balance assignments may not be used
  ,bsAssrt        :: Bool                                       -- ^ whether to check balance assertions
   -- mutable
  ,bsBalances     :: H.HashTable s AccountName MixedAmount      -- ^ running account balances, initially empty
  ,bsTransactions :: STArray s Integer Transaction              -- ^ a mutable array of the transactions being balanced
    -- (for efficiency ? journalBalanceTransactions says: not strictly necessary but avoids a sort at the end I think)
  }

-- | Access the current balancing state, and possibly modify the mutable bits,
-- lifting through the Except and Reader layers into the Balancing monad.
withRunningBalance :: (BalancingState s -> ST s a) -> Balancing s a
withRunningBalance f = ask >>= lift . lift . f

-- | Get this account's current exclusive running balance.
getRunningBalanceB :: AccountName -> Balancing s MixedAmount
getRunningBalanceB acc = withRunningBalance $ \BalancingState{bsBalances} -> do
  fromMaybe nullmixedamt <$> H.lookup bsBalances acc

-- | Add this amount to this account's exclusive running balance.
-- Returns the new running balance.
addToRunningBalanceB :: AccountName -> MixedAmount -> Balancing s MixedAmount
addToRunningBalanceB acc amt = withRunningBalance $ \BalancingState{bsBalances} -> do
  old <- fromMaybe nullmixedamt <$> H.lookup bsBalances acc
  let new = maPlus old amt
  H.insert bsBalances acc new
  return new

-- | Set this account's exclusive running balance to this amount.
-- Returns the change in exclusive running balance.
setRunningBalanceB :: AccountName -> MixedAmount -> Balancing s MixedAmount
setRunningBalanceB acc amt = withRunningBalance $ \BalancingState{bsBalances} -> do
  old <- fromMaybe nullmixedamt <$> H.lookup bsBalances acc
  H.insert bsBalances acc amt
  return $ maMinus amt old

-- | Set this account's exclusive running balance to whatever amount
-- makes its *inclusive* running balance (the sum of exclusive running
-- balances of this account and any subaccounts) be the given amount.
-- Returns the change in exclusive running balance.
setInclusiveRunningBalanceB :: AccountName -> MixedAmount -> Balancing s MixedAmount
setInclusiveRunningBalanceB acc newibal = withRunningBalance $ \BalancingState{bsBalances} -> do
  oldebal  <- fromMaybe nullmixedamt <$> H.lookup bsBalances acc
  allebals <- H.toList bsBalances
  let subsibal =  -- sum of any subaccounts' running balances
        maSum . map snd $ filter ((acc `isAccountNamePrefixOf`).fst) allebals
  let newebal = maMinus newibal subsibal
  H.insert bsBalances acc newebal
  return $ maMinus newebal oldebal

-- | Update (overwrite) this transaction in the balancing state.
updateTransactionB :: Transaction -> Balancing s ()
updateTransactionB t = withRunningBalance $ \BalancingState{bsTransactions}  ->
  void $ writeArray bsTransactions (tindex t) t

-- | Infer any missing amounts (to satisfy balance assignments and
-- to balance transactions) and check that all transactions balance
-- and (optional) all balance assertions pass. Or return an error message
-- (just the first error encountered).
--
-- Assumes journalInferCommodityStyles has been called, since those
-- affect transaction balancing.
--
-- This does multiple things at once because amount inferring, balance
-- assignments, balance assertions and posting dates are interdependent.
journalBalanceTransactions :: BalancingOpts -> Journal -> Either String Journal
journalBalanceTransactions bopts' j' =
  let
    -- ensure transactions are numbered, so we can store them by number
    j@Journal{jtxns=ts} = journalNumberTransactions j'
    -- display precisions used in balanced checking
    styles = Just $ journalCommodityStyles j
    bopts = bopts'{commodity_styles_=styles}
    -- balance assignments will not be allowed on these
    txnmodifieraccts = S.fromList . map (paccount . tmprPosting) . concatMap tmpostingrules $ jtxnmodifiers j
  in
    runST $ do
      -- We'll update a mutable array of transactions as we balance them,
      -- not strictly necessary but avoids a sort at the end I think.
      balancedtxns <- newListArray (1, toInteger $ length ts) ts

      -- Infer missing posting amounts, check transactions are balanced,
      -- and check balance assertions. This is done in two passes:
      runExceptT $ do

        -- 1. Step through the transactions, balancing the ones which don't have balance assignments
        -- and leaving the others for later. The balanced ones are split into their postings.
        -- The postings and not-yet-balanced transactions remain in the same relative order.
        psandts :: [Either Posting Transaction] <- fmap concat $ forM ts $ \case
          t | null $ assignmentPostings t -> case balanceTransaction bopts t of
              Left  e  -> throwError e
              Right t' -> do
                lift $ writeArray balancedtxns (tindex t') t'
                return $ map Left $ tpostings t'
          t -> return [Right t]

        -- 2. Sort these items by date, preserving the order of same-day items,
        -- and step through them while keeping running account balances,
        runningbals <- lift $ H.newSized (length $ journalAccountNamesUsed j)
        flip runReaderT (BalancingState styles txnmodifieraccts (not $ ignore_assertions_ bopts) runningbals balancedtxns) $ do
          -- performing balance assignments in, and balancing, the remaining transactions,
          -- and checking balance assertions as each posting is processed.
          void $ mapM' balanceTransactionAndCheckAssertionsB $ sortOn (either postingDate tdate) psandts

        ts' <- lift $ getElems balancedtxns
        return j{jtxns=ts'}

-- | This function is called statefully on each of a date-ordered sequence of
-- 1. fully explicit postings from already-balanced transactions and
-- 2. not-yet-balanced transactions containing balance assignments.
-- It executes balance assignments and finishes balancing the transactions,
-- and checks balance assertions on each posting as it goes.
-- An error will be thrown if a transaction can't be balanced
-- or if an illegal balance assignment is found (cf checkIllegalBalanceAssignment).
-- Transaction prices are removed, which helps eg balance-assertions.test: 15. Mix different commodities and assignments.
-- This stores the balanced transactions in case 2 but not in case 1.
balanceTransactionAndCheckAssertionsB :: Either Posting Transaction -> Balancing s ()
balanceTransactionAndCheckAssertionsB (Left p@Posting{}) =
  -- update the account's running balance and check the balance assertion if any
  void . addAmountAndCheckAssertionB $ postingStripPrices p
balanceTransactionAndCheckAssertionsB (Right t@Transaction{tpostings=ps}) = do
  -- make sure we can handle the balance assignments
  mapM_ checkIllegalBalanceAssignmentB ps
  -- for each posting, infer its amount from the balance assignment if applicable,
  -- update the account's running balance and check the balance assertion if any
  ps' <- mapM (addOrAssignAmountAndCheckAssertionB . postingStripPrices) ps
  -- infer any remaining missing amounts, and make sure the transaction is now fully balanced
  styles <- R.reader bsStyles
  case balanceTransactionHelper defbalancingopts{commodity_styles_=styles} t{tpostings=ps'} of
    Left err -> throwError err
    Right (t', inferredacctsandamts) -> do
      -- for each amount just inferred, update the running balance
      mapM_ (uncurry addToRunningBalanceB) inferredacctsandamts
      -- and save the balanced transaction.
      updateTransactionB t'

-- | If this posting has an explicit amount, add it to the account's running balance.
-- If it has a missing amount and a balance assignment, infer the amount from, and
-- reset the running balance to, the assigned balance.
-- If it has a missing amount and no balance assignment, leave it for later.
-- Then test the balance assertion if any.
addOrAssignAmountAndCheckAssertionB :: Posting -> Balancing s Posting
addOrAssignAmountAndCheckAssertionB p@Posting{paccount=acc, pamount=amt, pbalanceassertion=mba}
  -- an explicit posting amount
  | hasAmount p = do
      newbal <- addToRunningBalanceB acc amt
      whenM (R.reader bsAssrt) $ checkBalanceAssertionB p newbal
      return p

  -- no explicit posting amount, but there is a balance assignment
  | Just BalanceAssertion{baamount,batotal,bainclusive} <- mba = do
      newbal <- if batotal
                   -- a total balance assignment (==, all commodities)
                   then return $ mixedAmount baamount
                   -- a partial balance assignment (=, one commodity)
                   else do
                     oldbalothercommodities <- filterMixedAmount ((acommodity baamount /=) . acommodity) <$> getRunningBalanceB acc
                     return $ maAddAmount oldbalothercommodities baamount
      diff <- (if bainclusive then setInclusiveRunningBalanceB else setRunningBalanceB) acc newbal
      let p' = p{pamount=diff, poriginal=Just $ originalPosting p}
      whenM (R.reader bsAssrt) $ checkBalanceAssertionB p' newbal
      return p'

  -- no explicit posting amount, no balance assignment
  | otherwise = return p

-- | Add the posting's amount to its account's running balance, and
-- optionally check the posting's balance assertion if any.
-- The posting is expected to have an explicit amount (otherwise this does nothing).
-- Adding and checking balance assertions are tightly paired because we
-- need to see the balance as it stands after each individual posting.
addAmountAndCheckAssertionB :: Posting -> Balancing s Posting
addAmountAndCheckAssertionB p | hasAmount p = do
  newbal <- addToRunningBalanceB (paccount p) $ pamount p
  whenM (R.reader bsAssrt) $ checkBalanceAssertionB p newbal
  return p
addAmountAndCheckAssertionB p = return p

-- | Check a posting's balance assertion against the given actual balance, and
-- return an error if the assertion is not satisfied.
-- If the assertion is partial, unasserted commodities in the actual balance
-- are ignored; if it is total, they will cause the assertion to fail.
checkBalanceAssertionB :: Posting -> MixedAmount -> Balancing s ()
checkBalanceAssertionB p@Posting{pbalanceassertion=Just (BalanceAssertion{baamount,batotal})} actualbal =
    forM_ (baamount : otheramts) $ \amt -> checkBalanceAssertionOneCommodityB p amt actualbal
  where
    assertedcomm = acommodity baamount
    otheramts | batotal   = map (\a -> a{aquantity=0}) . amountsRaw
                          $ filterMixedAmount ((/=assertedcomm).acommodity) actualbal
              | otherwise = []
checkBalanceAssertionB _ _ = return ()

-- | Does this (single commodity) expected balance match the amount of that
-- commodity in the given (multicommodity) actual balance ? If not, returns a
-- balance assertion failure message based on the provided posting.  To match,
-- the amounts must be exactly equal (display precision is ignored here).
-- If the assertion is inclusive, the expected amount is compared with the account's
-- subaccount-inclusive balance; otherwise, with the subaccount-exclusive balance.
checkBalanceAssertionOneCommodityB :: Posting -> Amount -> MixedAmount -> Balancing s ()
checkBalanceAssertionOneCommodityB p@Posting{paccount=assertedacct} assertedamt actualbal = do
  let isinclusive = maybe False bainclusive $ pbalanceassertion p
  actualbal' <-
    if isinclusive
    then
      -- sum the running balances of this account and any of its subaccounts seen so far
      withRunningBalance $ \BalancingState{bsBalances} ->
        H.foldM
          (\ibal (acc, amt) -> return $
            if assertedacct==acc || assertedacct `isAccountNamePrefixOf` acc then maPlus ibal amt else ibal)
          nullmixedamt
          bsBalances
    else return actualbal
  let
    assertedcomm    = acommodity assertedamt
    actualbalincomm = headDef nullamt . amountsRaw . filterMixedAmountByCommodity assertedcomm $ actualbal'
    pass =
      aquantity
        -- traceWith (("asserted:"++).showAmountDebug)
        assertedamt ==
      aquantity
        -- traceWith (("actual:"++).showAmountDebug)
        actualbalincomm

    errmsg = printf (unlines
                  [ "balance assertion: %s",
                    "\nassertion details:",
                    "date:       %s",
                    "account:    %s%s",
                    "commodity:  %s",
                    -- "display precision:  %d",
                    "calculated: %s", -- (at display precision: %s)",
                    "asserted:   %s", -- (at display precision: %s)",
                    "difference: %s"
                  ])
      (case ptransaction p of
         Nothing -> "?" -- shouldn't happen
         Just t ->  printf "%s\ntransaction:\n%s"
                      (showGenericSourcePos pos)
                      (textChomp $ showTransaction t)
                      :: String
                      where
                        pos = baposition $ fromJust $ pbalanceassertion p
      )
      (showDate $ postingDate p)
      (T.unpack $ paccount p) -- XXX pack
      (if isinclusive then " (and subs)" else "" :: String)
      assertedcomm
      -- (asprecision $ astyle actualbalincommodity)  -- should be the standard display precision I think
      (show $ aquantity actualbalincomm)
      -- (showAmount actualbalincommodity)
      (show $ aquantity assertedamt)
      -- (showAmount assertedamt)
      (show $ aquantity assertedamt - aquantity actualbalincomm)

  unless pass $ throwError errmsg

-- | Throw an error if this posting is trying to do an illegal balance assignment.
checkIllegalBalanceAssignmentB :: Posting -> Balancing s ()
checkIllegalBalanceAssignmentB p = do
  checkBalanceAssignmentPostingDateB p
  checkBalanceAssignmentUnassignableAccountB p

-- XXX these should show position. annotateErrorWithTransaction t ?

-- | Throw an error if this posting is trying to do a balance assignment and
-- has a custom posting date (which makes amount inference too hard/impossible).
checkBalanceAssignmentPostingDateB :: Posting -> Balancing s ()
checkBalanceAssignmentPostingDateB p =
  when (hasBalanceAssignment p && isJust (pdate p)) $
    throwError . T.unpack $ T.unlines
      ["postings which are balance assignments may not have a custom date."
      ,"Please write the posting amount explicitly, or remove the posting date:"
      ,""
      ,maybe (T.unlines $ showPostingLines p) showTransaction $ ptransaction p
      ]

-- | Throw an error if this posting is trying to do a balance assignment and
-- the account does not allow balance assignments (eg because it is referenced
-- by a transaction modifier, which might generate additional postings to it).
checkBalanceAssignmentUnassignableAccountB :: Posting -> Balancing s ()
checkBalanceAssignmentUnassignableAccountB p = do
  unassignable <- R.asks bsUnassignable
  when (hasBalanceAssignment p && paccount p `S.member` unassignable) $
    throwError . T.unpack $ T.unlines
      ["balance assignments cannot be used with accounts which are"
      ,"posted to by transaction modifier rules (auto postings)."
      ,"Please write the posting amount explicitly, or remove the rule."
      ,""
      ,"account: " <> paccount p
      ,""
      ,"transaction:"
      ,""
      ,maybe (T.unlines $ showPostingLines p) showTransaction $ ptransaction p
      ]

-- lenses

makeHledgerClassyLenses ''BalancingOpts

-- tests

tests_Balancing :: TestTree
tests_Balancing =
  testGroup "Balancing" [

      testCase "inferBalancingAmount" $ do
         (fst <$> inferBalancingAmount M.empty nulltransaction) @?= Right nulltransaction
         (fst <$> inferBalancingAmount M.empty nulltransaction{tpostings = ["a" `post` usd (-5), "b" `post` missingamt]}) @?=
           Right nulltransaction{tpostings = ["a" `post` usd (-5), "b" `post` usd 5]}
         (fst <$> inferBalancingAmount M.empty nulltransaction{tpostings = ["a" `post` usd (-5), "b" `post` (eur 3 @@ usd 4), "c" `post` missingamt]}) @?=
           Right nulltransaction{tpostings = ["a" `post` usd (-5), "b" `post` (eur 3 @@ usd 4), "c" `post` usd 1]}

    , testGroup "balanceTransaction" [
         testCase "detect unbalanced entry, sign error" $
          assertLeft
            (balanceTransaction defbalancingopts
               (Transaction
                  0
                  ""
                  nullsourcepos
                  (fromGregorian 2007 01 28)
                  Nothing
                  Unmarked
                  ""
                  "test"
                  ""
                  []
                  [posting {paccount = "a", pamount = mixedAmount (usd 1)}, posting {paccount = "b", pamount = mixedAmount (usd 1)}]))
        ,testCase "detect unbalanced entry, multiple missing amounts" $
          assertLeft $
             balanceTransaction defbalancingopts
               (Transaction
                  0
                  ""
                  nullsourcepos
                  (fromGregorian 2007 01 28)
                  Nothing
                  Unmarked
                  ""
                  "test"
                  ""
                  []
                  [ posting {paccount = "a", pamount = missingmixedamt}
                  , posting {paccount = "b", pamount = missingmixedamt}
                  ])
        ,testCase "one missing amount is inferred" $
          (pamount . last . tpostings <$>
           balanceTransaction defbalancingopts
             (Transaction
                0
                ""
                nullsourcepos
                (fromGregorian 2007 01 28)
                Nothing
                Unmarked
                ""
                ""
                ""
                []
                [posting {paccount = "a", pamount = mixedAmount (usd 1)}, posting {paccount = "b", pamount = missingmixedamt}])) @?=
          Right (mixedAmount $ usd (-1))
        ,testCase "conversion price is inferred" $
          (pamount . head . tpostings <$>
           balanceTransaction defbalancingopts
             (Transaction
                0
                ""
                nullsourcepos
                (fromGregorian 2007 01 28)
                Nothing
                Unmarked
                ""
                ""
                ""
                []
                [ posting {paccount = "a", pamount = mixedAmount (usd 1.35)}
                , posting {paccount = "b", pamount = mixedAmount (eur (-1))}
                ])) @?=
          Right (mixedAmount $ usd 1.35 @@ eur 1)
        ,testCase "balanceTransaction balances based on cost if there are unit prices" $
          assertRight $
          balanceTransaction defbalancingopts
            (Transaction
               0
               ""
               nullsourcepos
               (fromGregorian 2011 01 01)
               Nothing
               Unmarked
               ""
               ""
               ""
               []
               [ posting {paccount = "a", pamount = mixedAmount $ usd 1 `at` eur 2}
               , posting {paccount = "a", pamount = mixedAmount $ usd (-2) `at` eur 1}
               ])
        ,testCase "balanceTransaction balances based on cost if there are total prices" $
          assertRight $
          balanceTransaction defbalancingopts
            (Transaction
               0
               ""
               nullsourcepos
               (fromGregorian 2011 01 01)
               Nothing
               Unmarked
               ""
               ""
               ""
               []
               [ posting {paccount = "a", pamount = mixedAmount $ usd 1 @@ eur 1}
               , posting {paccount = "a", pamount = mixedAmount $ usd (-2) @@ eur (-1)}
               ])
        ]
    , testGroup "isTransactionBalanced" [
         testCase "detect balanced" $
          assertBool "" $
          isTransactionBalanced defbalancingopts $
          Transaction
            0
            ""
            nullsourcepos
            (fromGregorian 2009 01 01)
            Nothing
            Unmarked
            ""
            "a"
            ""
            []
            [ posting {paccount = "b", pamount = mixedAmount (usd 1.00)}
            , posting {paccount = "c", pamount = mixedAmount (usd (-1.00))}
            ]
        ,testCase "detect unbalanced" $
          assertBool "" $
          not $
          isTransactionBalanced defbalancingopts $
          Transaction
            0
            ""
            nullsourcepos
            (fromGregorian 2009 01 01)
            Nothing
            Unmarked
            ""
            "a"
            ""
            []
            [ posting {paccount = "b", pamount = mixedAmount (usd 1.00)}
            , posting {paccount = "c", pamount = mixedAmount (usd (-1.01))}
            ]
        ,testCase "detect unbalanced, one posting" $
          assertBool "" $
          not $
          isTransactionBalanced defbalancingopts $
          Transaction
            0
            ""
            nullsourcepos
            (fromGregorian 2009 01 01)
            Nothing
            Unmarked
            ""
            "a"
            ""
            []
            [posting {paccount = "b", pamount = mixedAmount (usd 1.00)}]
        ,testCase "one zero posting is considered balanced for now" $
          assertBool "" $
          isTransactionBalanced defbalancingopts $
          Transaction
            0
            ""
            nullsourcepos
            (fromGregorian 2009 01 01)
            Nothing
            Unmarked
            ""
            "a"
            ""
            []
            [posting {paccount = "b", pamount = mixedAmount (usd 0)}]
        ,testCase "virtual postings don't need to balance" $
          assertBool "" $
          isTransactionBalanced defbalancingopts $
          Transaction
            0
            ""
            nullsourcepos
            (fromGregorian 2009 01 01)
            Nothing
            Unmarked
            ""
            "a"
            ""
            []
            [ posting {paccount = "b", pamount = mixedAmount (usd 1.00)}
            , posting {paccount = "c", pamount = mixedAmount (usd (-1.00))}
            , posting {paccount = "d", pamount = mixedAmount (usd 100), ptype = VirtualPosting}
            ]
        ,testCase "balanced virtual postings need to balance among themselves" $
          assertBool "" $
          not $
          isTransactionBalanced defbalancingopts $
          Transaction
            0
            ""
            nullsourcepos
            (fromGregorian 2009 01 01)
            Nothing
            Unmarked
            ""
            "a"
            ""
            []
            [ posting {paccount = "b", pamount = mixedAmount (usd 1.00)}
            , posting {paccount = "c", pamount = mixedAmount (usd (-1.00))}
            , posting {paccount = "d", pamount = mixedAmount (usd 100), ptype = BalancedVirtualPosting}
            ]
        ,testCase "balanced virtual postings need to balance among themselves (2)" $
          assertBool "" $
          isTransactionBalanced defbalancingopts $
          Transaction
            0
            ""
            nullsourcepos
            (fromGregorian 2009 01 01)
            Nothing
            Unmarked
            ""
            "a"
            ""
            []
            [ posting {paccount = "b", pamount = mixedAmount (usd 1.00)}
            , posting {paccount = "c", pamount = mixedAmount (usd (-1.00))}
            , posting {paccount = "d", pamount = mixedAmount (usd 100), ptype = BalancedVirtualPosting}
            , posting {paccount = "3", pamount = mixedAmount (usd (-100)), ptype = BalancedVirtualPosting}
            ]
        ]

  ,testGroup "journalBalanceTransactions" [

     testCase "missing-amounts" $ do
      let ej = journalBalanceTransactions defbalancingopts $ samplejournalMaybeExplicit False
      assertRight ej
      journalPostings <$> ej @?= Right (journalPostings samplejournal)

    ,testCase "balance-assignment" $ do
      let ej = journalBalanceTransactions defbalancingopts $
            --2019/01/01
            --  (a)            = 1
            nulljournal{ jtxns = [
              transaction (fromGregorian 2019 01 01) [ vpost' "a" missingamt (balassert (num 1)) ]
            ]}
      assertRight ej
      let Right j = ej
      (jtxns j & head & tpostings & head & pamount & amountsRaw) @?= [num 1]

    ,testCase "same-day-1" $ do
      assertRight $ journalBalanceTransactions defbalancingopts $
            --2019/01/01
            --  (a)            = 1
            --2019/01/01
            --  (a)          1 = 2
            nulljournal{ jtxns = [
               transaction (fromGregorian 2019 01 01) [ vpost' "a" missingamt (balassert (num 1)) ]
              ,transaction (fromGregorian 2019 01 01) [ vpost' "a" (num 1)    (balassert (num 2)) ]
            ]}

    ,testCase "same-day-2" $ do
      assertRight $ journalBalanceTransactions defbalancingopts $
            --2019/01/01
            --    (a)                  2 = 2
            --2019/01/01
            --    b                    1
            --    a
            --2019/01/01
            --    a                    0 = 1
            nulljournal{ jtxns = [
               transaction (fromGregorian 2019 01 01) [ vpost' "a" (num 2)    (balassert (num 2)) ]
              ,transaction (fromGregorian 2019 01 01) [
                 post' "b" (num 1)     Nothing
                ,post' "a"  missingamt Nothing
              ]
              ,transaction (fromGregorian 2019 01 01) [ post' "a" (num 0)     (balassert (num 1)) ]
            ]}

    ,testCase "out-of-order" $ do
      assertRight $ journalBalanceTransactions defbalancingopts $
            --2019/1/2
            --  (a)    1 = 2
            --2019/1/1
            --  (a)    1 = 1
            nulljournal{ jtxns = [
               transaction (fromGregorian 2019 01 02) [ vpost' "a" (num 1)    (balassert (num 2)) ]
              ,transaction (fromGregorian 2019 01 01) [ vpost' "a" (num 1)    (balassert (num 1)) ]
            ]}

    ]

    ,testGroup "commodityStylesFromAmounts" $ [

      -- Journal similar to the one on #1091:
      -- 2019/09/24
      --     (a)            1,000.00
      -- 
      -- 2019/09/26
      --     (a)             1000,000
      --
      testCase "1091a" $ do
        commodityStylesFromAmounts [
           nullamt{aquantity=1000, astyle=AmountStyle L False (Precision 3) (Just ',') Nothing}
          ,nullamt{aquantity=1000, astyle=AmountStyle L False (Precision 2) (Just '.') (Just (DigitGroups ',' [3]))}
          ]
         @?=
          -- The commodity style should have period as decimal mark
          -- and comma as digit group mark.
          Right (M.fromList [
            ("", AmountStyle L False (Precision 3) (Just '.') (Just (DigitGroups ',' [3])))
          ])
        -- same journal, entries in reverse order
      ,testCase "1091b" $ do
        commodityStylesFromAmounts [
           nullamt{aquantity=1000, astyle=AmountStyle L False (Precision 2) (Just '.') (Just (DigitGroups ',' [3]))}
          ,nullamt{aquantity=1000, astyle=AmountStyle L False (Precision 3) (Just ',') Nothing}
          ]
         @?=
          -- The commodity style should have period as decimal mark
          -- and comma as digit group mark.
          Right (M.fromList [
            ("", AmountStyle L False (Precision 3) (Just '.') (Just (DigitGroups ',' [3])))
          ])

     ]

  ]